This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We sought an in vitro primate model for serotonin neurons. Using the rhesus embryonic stem cell (ESC) line 366.4, a protocol was developed which generates a high percentage of serotonin neurons as determined by immunocytochemistry for tryptophan hydroxylase and the serotonin reuptake transporter. In addition, the ESC-derived neurons express estrogen receptor beta (ERbeta) and progesterone receptors (PR) in a manner similar to serotonin neurons in the macaque brain. We now seek to characterize physiological functions of these neurons and to examine the gene expression profile during each stage of differentiation. This culture system will reduce our need for primates and enable cellular and molecular studies of the primate serotonin system that are not currently feasible.